1. Field of the Invention
The present invention relates to fluid dispensers and more particularly to dispensers for relatively thick mixtures such as sauces for foods sometimes containing lumps. The invention finds particular utility in dispensing materials such as tomato sauce onto pizza crusts in an assembly line production where a plurality of pizza crusts are caused to move past the dispenser and to have an fixed amount of tomato sauce distributed over their surface.
2. Description of the Prior Art
Examples of dispensers presently known in the art may be seen in, for example, U.S. Pat. No. 3,602,154 issued Aug. 31, 1971 to E. H. Schimkat et al. Such devices employ a supply tank which feeds the food products such as pizza sauce to a plurality of pistons which force the sauce into a plurality of valves located above a dispensing area. A conveyor belt moves the pizza crusts to the dispensing area and the pizzas are then lifted and rotated underneath the valve to apply the sauce thereto. Such apparatus is extremely difficult to manage, has no ability to easily change the size of the pizzas being processed and requires that the pizzas be evenly placed on the conveyor system at known location in order to operate properly.
The assignee of the present invention has devised a system in which the pizzas may moved under a dispensing area past a plurality of detectors which sense their presence and a signal is provided to a computer which also receives an input indicative of the speed of the conveyor and accordingly knows the moment that the leading edge of the pizza crust arrives in a dispensing area. The computer controls the opening of the appropriate valves as the pizza crust moves through the dispensing area so that the sauce from the tank is pumped through one or more orifices and onto the crusts for the length of time necessary to lay a plurality of strips thereon. As the pizza crust moves out of the dispensing area, the appropriate valves are closed and thereafter the strips of sauce tend to flow together as the crust continues to move so as to leave a relatively even surface of sauce thereon.
Systems such as described above have encountered a number of problems particularly when the fluid is a tomato sauce to be dispensed onto an object such as a pizza crust. For example, tomato sauce is known to act in a thixotropic manner; that is having a tendency to resist flowing until it is agitated to start. Accordingly, low flow usually occurs upon starting and uneven flow of sauce to crust results. The importance of this is found in fact that previous systems require a 20% or more excess target flow to assure at least a predetermined quantity of sauce is provided to each pizza. Not only is the extra cost of sauce significant but inconsistent pizzas result. It has been found that the pizzas which have excess sauce variation do not meet customer expectations of a uniform product. Accordingly, it is extremely desirable to provide sauce to the pizzas in a consistent manner.
Another problem encountered in prior art systems is blockage in one or more nozzles because of the fact that the sauces being dispensed may contain particles of spice or tomato. When this occurs, a number of pizza crusts may have one or more strips of sauce missing before an operator notices the discrepancy and corrects the blocked valve by applying an excess pressure thereto to blow the blockage away. Because of this, time has been wasted and several pizza crusts have to be discarded. To minimize this problem, the prior art has needed to have larger than desirable valve nozzles and this has produced a poor spread of sauce.
Another difficulty encountered in the prior art arises when there is insufficient pressure to assure continuous full flow conditions. When this occurs, one or more of the valves do not receive enough sauce and uneven and inconsistent applications result.
Prior art dispensing systems have also been unable to handle different set-up arrangements and can handle only one pizza size at a time. It is desirable to be able to sometimes use a single lane, sometimes two and sometimes three or more lanes and to handle different size crusts (5,7,9,11 & 12 inch pizzas are common) without having to change the valve positions.